1. Field of the Invention
The present invention relates generally to the treatment of disease and, more particularly, to the treatment of diseases associated with receptor-operated calcium channels, including the treatment of hypertension, atherosclerosis, atherogenesis, thrombosis, vasospasm, and the consequences of these conditions.
Agonist-mediated increases in intracellular calcium in mammalian cells can occur via multiple mechanisms, most notably increased conductance of Ca.sup.2+ ions through voltage-operated calcium channels (VOCCs) and receptor-operated calcium channels (ROCCs), both being located in the plasma membrane.
The VOCCs were the first identified in cardiac muscle and their characterization were greatly facilitated by the discovery of the highly sensitive and specific dihydropyridine antagonists. Fleckenstein et al., Am. J. Cardiol. (1987)59:177B-187B. These channels occur primarily in so-called electrically excitable cells and have been studied extensively in cardiac, smooth, and skeletal muscle. Channel opening, or more precisely, the probability that specified numbers of calcium channels are biophysically in the open state, is directly related to the potential difference across the plasma membrane. Depolarization increases the probability of the existence of VOCCs in the open state, whereas hyperpolarization results in the opposite, that VOCCs are likely to be closed.
The ROCCs, on the other hand are insensitive to changes in membrane potential and although sensitivity to dihydropyridine antagonists have been reported, the concentration required for significant blockade are orders of magnitude greater than those required for antagonism of VOCCs. ROCCs are activated by specific ligands and have been identified in all mammalian cell types examined including electrically excitable cells, e.g. cardiac and vascular smooth muscle. ROCCs have been identified in cells not ordinarily thought of being electrically excitable (Table 1).
The activity of ROCCs appear to be modulated primarily through agonist interaction with specific cell surface receptors with consequent phosphinositide breakdown and induction by inositol phosphates, e.g. inositol trisphosphate and inositol tetrakisphosphate, and activation of calcium entry via ROCCs. Ligands that transmit their biological signals by mechanisms involving calcium entry via ROCCs produce a transient increase in intracellular calcium concentration (Ca.sup.2+ !i) typified by a characteristic time-dependent kinetic form, regardless of the particular chemical agonist or the cell (tissue) type.
TABLE I ______________________________________ Disease processes and potential sites of lesions where receptor-operated calcium channel antagonists are expected to function to offset the particular lesion(s) Pathophysiologic processes, Disease states Tissues Neurohumoral agents ______________________________________ Atherogenesis, VSM, endothelium growth factors, A II Atherosclerosis, endothelin, cytokines, Vasospasm, Angina PDGF, thrombin Pectoris Restenosis after VSM, endothelium PDGF, growth factors angioplasty Thrombosis & VSM, platelets PDGF, thrombin, A II, infarction endothelium, EGF, TGF-beta Hypertension VSM cell, endothelium, vasopressors, EDRF, autononic innervation, neurotransmitters, juxtaglomerular endothelins Neoplasia and various transforming growth, oncogenesis factors, endothelin, PDGF Immunodeficient T cell, B cell, immune response conditions mast cells, eosinophil modifiers, cytokines neutrophil, macrohage chemotactic peptides Wound-healing mesenchyme and other growth factors, cell cells adhesion molecules Reactive airway bronchial VSM cell histamine, endothelin, disease, asthma & endothelium, mast beta-2 agonists, allergy cells, cromolyn Neural dysfunction glial cells, others neurotransmitters glioblastoma nerve growth and other factors, endothelin Schizophrenia CNS endothelin Encephalopathy CNS neuropeptides, amino acids, nitric oxide Memory dysfuncton CNS, other neural cells neurotransmitters Organogenesis various colony-stimulating and chemotactic factors, neuropeptides Endometriosis endometrial cells PDGF, other growth factors Algesia CNS kinin/kininogen modulators ______________________________________ VSM = vascular smooth muscle; EDRF = endotheliumderived relaxing factor; TGFbeta = transforming growth factor; A II = angiotensin II; EGF = epidermal growth factor
Subsequent to agonist-receptor binding, depending on the activator, there is a sharp initial spike in Ca.sup.2+ !i either immediately or after a delay followed by a slow decay in the calcium signal, which may be followed in some cases by oscillatory excursions in the calcium signal. Depending on cell-type or agonist, this general form has subtle but important variations, and may represent different subtypes of receptor-operated channels (see "Experimental Findings" below, and Ref: Rink, FEBS Lett, 1990).
A first aspect of the invention focuses on two physiological ligands that function via modulation of ROCCs and are implicated in the pathogenesis of hypertension, atherogenesis and atherosclerosis and other vasculoproliferative disease.
A second aspect of the invention includes the general implications of the role of ROCCs in the pathophysiological derangements in a variety of cellular functions, including those involving, neoplasia, immune response modification, endocrine and exocrine dysfunction, neuropsychiatric disease, wound-healing, and cell growth and proliferation in diverse organ systems. These vast implications will be disclosed in the context of small neurohumoral peptides, particularly platelet-derived growth factor (PDGF) and bradykinin.
A further aspect of the invention includes the utility of the subject use of thiazole compounds as antagonists for ROCCs in the further illucidation of ROCC operation.
A still further aspect of the invention includes the use of thiazole compounds in the treatment of disease in humans such as atherosclerosis.